Package stack via bottom leaded plastic (BLP) packaging

ABSTRACT

A packaged semiconductor device has bottom surface leads having portions of the package adjacent the lead edges excised. The outer leads may take the form of inverted-J leads, short stub leads, vertically bent leads-in-grooves, or may be entirely eliminated. Lead connections are on the bottom package surface, over the top package surface, and/or on the sides and ends of the package, enabling vertical stacking of the devices and simultaneous/alternative coplanar horizontal connections to other semiconductor devices, circuit boards, etc. A mold assembly with a castellated inner surface forms a package with alternating grooves and columns for holding side and end electrical connection surfaces.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 08/890,414,filed Jul. 9, 1997, and now U.S. Pat. No. 5,986,209.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor devices. Moreparticularly, the invention pertains to surface and external leadconfigurations of packaged semiconductor devices for electricalconnection to other apparatus.

2. State of the Art

The continuing miniaturization of semiconductor devices is crucial tothe electronics industry. Numerous improvements have contributed to theindustry growth, including the development of leads-over-chips (LOC)assemblies and their inverse, chip-over-leads (COL) configurations.Thus, the die-attach support was eliminated and lead length was reduced,decreasing the package size. Further developments have included packageddevices in which a plurality of dies and leads therefor are encapsulatedwithin a single package. Such is well illustrated, for example, in U.S.Pat. No. 5,331,235 of Chun, U.S. Pat. No. 5,471,369 of Honda et al.,U.S. Pat. No. 5,483,024 of Russell et al., U.S. Pat. No. 5,498,902 ofHara, U.S. Pat. No. 5,508,565 of Hatakeyama et al., U.S. Pat. No.5,530,292 of Waki et al., and U.S. Pat. No. 5,572,068 of Chun.

While such developments have filled a need, there remain applicationswherein it is desirable to electrically attach separate, packagedsemiconductor devices to each other, and to circuit boards, incombinations providing the desired results. This focuses our attentionon the external electrical connections of the package by which it may beconnected to other packaged devices, circuit boards, various electricalconduits, and a wide variety of electrical apparatuses.

The state of the art is illustrated by the representative prior artsemiconductor devices shown in drawing FIGS. 1-4.

A representative example of a known packaged multi-chip semiconductordevice 10 of the piggy-back type is shown in drawing FIGS. 1 and 2. Aleads-over-chip (LOC) type construction with a small-outline-J-lead(SOJ) type package is depicted. The device includes a semiconductor chipor die 12 partially overcovered with an insulating layer(s) 14 such aspolyimide. The die 12 includes a plurality of pads 16, each of which iselectrically connected to a wire 18 whose opposite end is electricallyconnected to an end of an inner lead 20 of a leadframe. The die 12,insulative layers 14, wires 18, and inner leads 20 are enclosed inplastic 22, typically by a transfer molding process.

As shown in drawing FIG. 2, several packaged devices 10 of drawing FIG.1 may be stacked with their outer leads 24 connected by e.g. solderingto form a multi-chip package 26. As indicated, device 10B is superposedon device 10A and corresponding outer leads 24A and 24B of the devicesare joined by soldering to provide a piggy-back type of package 26. Theend portions 28 of the outer leads 24B are joined to the outer leads24A.

This type of construction has several disadvantages. First, the outerleads 24B of the superposed device 10B must be bent differently fromouter leads 24A of the underlying device 10A. Thus, the devices 10A and10B cannot be interchanged, and the outer leads 24B of device 10B arenot configured for attachment to a PCB.

In addition, each device 10C, 10D (not shown) to be stacked atop device10B requires a different outer lead configuration to enable properjoining of the stacked devices.

Turning now to drawing FIG. 3, a prior art semiconductor device 30 isdepicted in which two dies 12C, 12D are combined, face-to-face, andjoined to opposing sides of a single leadframe 32. The inner lead ends34A which approach the electrical pads 16 from one side are positionedbetween the inner lead ends 34B which approach the pads 16 from theopposite side. Layers 38 of insulative material separate the dies 12C,12D and leadframe 32 from each other generally. The combination of dies12C, 12D and the attached leadframe 32 is encapsulated by plastic 22within a single small-outline-J-lead (SOJ) package with conventionalouter J-leads 36.

Drawing FIG. 4 illustrates a prior art semiconductor device 40 shown inU.S. Pat. No. 5,554,886 of Song. The device 40 may be vertically stackedin multiple units. A die 12 is wire-bonded to leads 42 of a leadframe32. The inner leads 42 are configured to have metal laminates 43 joinedthereto, wherein surface portions 44 of the laminates are coplanar witha first major surface 46 of the plastic package 48 and are meant tocomprise bond areas for solder bonding to additional packages. The outerleads 36 have ends 52 which are formed to be parallel to the secondmajor surface 50, opposite to first major surface 46. Each lead end 52has a surface 54 for bonding to a circuit board or another devicepackage. Thus, multiple units of the device 40 may be stacked and havecorresponding surface portions 44 and 54 joined by solder.

Although the state of the art in package configuration is continuallyimproving, ever-increasing demands for further miniaturization, circuitcomplexity, production speed, reduced cost, product uniformity andreliability require further improvements in semiconductor deviceconnections by which the devices are readily electrically connected tocircuit boards, electrical apparatus, and each other.

In particular, the need for a semiconductor device capable of electricalconnection to a plurality of substrates, other devices, or variouselectrical apparatus in several configurations is presently needed.

SUMMARY OF THE INVENTION

In accordance with the invention, a package configuration for asemiconductor device is formed wherein the package size is reduced,stacking of packages is enabled without further modification of a loweror upper package, and the bonding of the device to electricalapparatuses is enhanced.

The external package configuration may be used with any internalconfiguration of dice, leads, insulative layers, heat sinks, die-to-leadconnections, etc. Thus, the internal assembly configuration may comprisea Leads-Over-Chip (LOC), Chip-Over-Leads (COL), single or multiple die,wire bonded leads and/or tape-automated bonding (TAB) as well as othervariations or combinations in construction.

A semiconductor package is formed in which the conductive lead has anintermediate portion which is encapsulated to have its exposed surfacecoplanar with the bottom surface of the package.

The outer lead is then an outward extension of the intermediate portion.The intermediate portion provides a bonding surface for joining to acircuit board, device, etc. In a further improvement of the invention,the encapsulant adjacent the edges of the intermediate lead portion isexcised to a depth equaling about 0.1-1.0 of the lead thickness. Theexcised portion may take a variety of configurations.

In another improvement, the semiconductor device is formed withsubsurface intermediate leads by which the leads of apparatus beingconnected are properly positioned by chamfered sides.

In another improvement, a semiconductor package is formed withcastellated sides and/or ends whereby the outer leads are bent upwardlyto fit in the castellation grooves, while extending slightly from thegrooves to provide bonding sites for electrical connection to otherdevices, etc. A mold assembly is described, infra, for producing thecastellated package.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is illustrated in the following figures, wherein theelements are not necessarily shown to scale:

FIG. 1 is a cross-sectional end view showing a construction of asemiconductor package of the prior art;

FIG. 2 is a cross-sectional end view showing a construction of a priorart multi-chip semiconductor device comprising a plurality of thepackages of FIG. 1 having their outer leads joined;

FIG. 3 is a cross-sectional end view of a construction of a multi-diesemiconductor package illustrative of the prior art;

FIG. 4 is a cross-sectional end view of a construction of a prior artsemiconductor package configured for multiple stacking;

FIG. 5 is a cross-sectional end view of two bottom-leaded packagedsemiconductor devices of the invention in a stacked configuration;

FIG. 6 is a partial bottom view of a bottom-leaded packagedsemiconductor device of the invention;

FIGS. 7A-7F are fragmentary enlarged cross-sectional side views throughsurface leads of differing embodiments of the bottom-leaded packagedsemiconductor devices of the invention;

FIG. 8 is a partial perspective view of another embodiment of abottom-leaded packaged semiconductor device of the invention;

FIG. 9 is a partial bottom view of the bottom-leaded packagedsemiconductor device of FIG. 8;

FIG. 10 is a partial perspective view of a further embodiment of abottom-leaded packaged semiconductor device of the invention withoutexternal leads; FIG. 11 is a partial bottom view of the bottom-leadedpackaged semiconductor device of FIG. 10;

FIG. 12 is a partial perspective view of an additional embodiment of abottom-leaded packaged semiconductor device of the invention;

FIG. 13 is a partial cross-sectional end view of the bottom-leadedpackaged semiconductor device of FIG. 12, as taken along line 13—13thereof;

FIG. 14 is a cross-sectional end view of an embodiment of thebottom-leaded packaged semiconductor device of the invention, as takenalong line 14—14 of FIG. 15;

FIG. 15 is a partial bottom view of the bottom-leaded packagedsemiconductor device of FIG. 14;

FIG. 16 is a partial end view of a transfer mold assembly forencapsulating a semiconductor device of the invention;

FIG. 17 is a partial end view of a transfer mold assembly of theinvention for encapsulating a semiconductor device with a castellatedpackage for enclosing outer leads; and

FIG. 18 is a partial cross-sectional plan view through the top plate ofa transfer mold assembly of the invention, as taken along line 18—18 ofFIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

A new semiconductor device and method of production thereof is providedby the invention. The semiconductor device is a small footprintsemiconductor package amenable to alternative conductive connection (a)in a multi-package vertical stacking configuration, (b) in amulti-package horizontal layout, and (c) to a printed circuit board(PCB) or other substrate.

With reference to the drawings of FIGS. 5-18 which describe the instantinvention, and particularly to FIGS. 5 and 6, a pair of semiconductordevices 100 are shown in cross-section. In each device 100, theparticular configuration of die 102, metallized lead frame 104, anddie-to-lead attach method may be any of the wide variety of knownconstructions in the art. As represented in FIGS. 5 and 6, achip-over-leads (COL) interior construction with inverted-J (IJ) outerleads 118 is shown with inner leads 106 conductively connected to diepads 108 by wires 110. An intermediate lead portion 112 is positionedduring encapsulation, e.g. transfer molding, to have a bottom leadsurface 114 generally coplanar with the bottom package surface 116 ofthe molded polymer package 120. The bottom lead surface 114 of theintermediate lead portion 112 of each lead comprises a bonding surfacefor conductive connection to a semiconductor device, a circuit board, orother conduit or electrical apparatus. Each lead is separated fromadjacent leads by a spacing 122 which may vary along the length of thelead. Preferably, the spacing 122 of the outer leads 118 is uniform.

As defined herein, the inner leads 106 are completely enclosed withinthe polymeric package 120. The outer leads 118 are completely outside ofthe package 120, and the intermediate lead portions 112, as formed, arewithin the bottom surface 116 of the package 120 and have a bottom leadsurface 114 exposed. The outer leads 118, shown as inverted-J (IJ)leads, of one device 100 may be joined to the intermediate lead portions112 of another device if desired, or either the outer leads orintermediate lead portions may be joined to a circuit board, otherelectrical conduits, or another electrical apparatus.

In accordance with certain embodiments of the invention, the spacing 122of the polymeric package 120 between the edges 124 of the intermediatelead portions 112 is partially cut away along and adjacent to theintermediate lead edges 124, exposing at least a portion of each edge.The excised portions 126 may take several cross-sectional forms, asdepicted generally in drawing FIGS. 7B, 7C, 7D or 7E.

Drawing FIG. 7A shows an intermediate lead portion 112 as formed alongwithin the molded polymer package 120. The bottom lead surface 114 isgenerally coplanar with the bottom package surface 116, depending uponthe precision of lead placement within the mold.

A thin coating of polymer will sometimes cover the bottom lead surface114 following removal of the device from the mold. In the manufacturingprocess, this coating will be subsequently removed to permit electricalconnection to a conductor. The top lead surface 128 and edges 124 areembedded in the package 120. The lead thickness 132 (typically betweenabout 0.5 and 3 mils) and the lead-to-lead spacing 122 (typically atleast about 2-3 mils) are indicated.

In one embodiment of the invention illustrated in drawing FIGS. 5 and 6,further shown in FIG. 7B, the lead-to-lead spacing 122 of the package120 is chamfered adjacent the full thickness 132 of each lead edge 124to expose the edges 124. The chamfer angle 130 of the excised chamferportions 126 may be between about 20 degrees and about 60 degrees,depending upon the available lead-to-lead distance between theintermediate lead portions 112.

In another embodiment shown in drawing FIG. 7C, the excised chamferportions 126 are shallower, extending to a depth 134 of as little asonly about ⅛ of the lead thickness 132. In drawing FIG. 7C, the depth134 is shown as about ½ of the lead thickness 132.

In drawing FIG. 7D, a greater portion of the lead-to-lead spacing 122 isremoved, by which an interlead ridge 136 of polymeric package materialextends downwardly to a distance 138 above the lead bottom surfaces 114.The ratio of distance 138 to lead thickness 132 may be between aboutzero and about 1.0, although a preferred ratio will be between about 0.1and about 0.6.

Drawing FIG. 7E shows another embodiment of the invention, in which thelead-to-lead spacing 122 is excised to a generally uniform depth 140.The ratio of depth 140 to the lead thickness 132 may be between about0.1 and about 0.8, but is preferably between about 0.1 and about 0.6.

In a further embodiment shown in drawing FIG. 7F, the excision includesnot only chamfered portions of the polymer package 120 but theintermediate lead portion 112 itself. Thus, the exposed lead bottomsurface 114 of the intermediate lead portion 112 is depressed into thepolymer package 120 a distance 45 which is up to about ½ of the originallead thickness 132. The distance 45 is thus at least ½ of the originallead thickness 132. The chamfer angle 130 may be between about 20degrees and 60 degrees, and more preferably about 30-45 degrees. Thisembodiment results in easier alignment of other leads which are to bejoined to the intermediate lead portions 112, the chamfer walls 149acting as retainers of the inserted lead edges, not shown.

Use of bottom leads along the sides of a semiconductor package, togetherwith excision of polymeric material from between the bottom leads,provides a number of improvements. For instance, the device 100 may beelectrically joined to another device, piggy-back style, which isalready joined to e.g. a circuit board. Or, the device occupies asmaller amount of area for mounting purposes on a substrate.

Turning now to drawing FIGS. 8 and 9, another version of the improvedsemiconductor device 100 is shown as a package 120 having a top surface117, a bottom surface 116, two sides 119, and ends 142. A generalcentral axis 144 passes lengthwise through the package 120.

In this version, the outer leads 118 are truncated horizontal extensionsof the intermediate bottom lead portions 112, extending a short distance146 outwardly, generally no more than about 8 to about 30 mils from thepackage sides 119. Preferably, distance 146 is between about 10 andabout 20 mils. The outer leads 118 have several surfaces which may beelectrically connected to other leads or apparatus, including the upperlead surface 148 and the bottom lead surface 114.

The semiconductor device 100 illustrated in drawing FIGS. 8 and 9 mayincorporate excision of the polymer package 120 along and adjacent theintermediate lead edges 124. Thus, any of the general excision shapesillustrated in drawing FIGS. 7B through 7E may be used, in addition tothe version of the invention illustrated in drawing FIG. 7A not havingexcised chamfer portions 126.

The semiconductor device 100 of drawing FIGS. 10 and 11 is similar tothat illustrated in drawing FIGS. 8 and 9, except that it has no “outer”or external leads. Thus, it has the smallest “footprint” of the variousembodiments, the footprint being merely the polymer package 120 itself.Electrical connections may be made between the bottom lead surfaces 114and/or the end surfaces 150 of the intermediate lead portions 112.

Like the embodiments previously described, the embodiment illustrated indrawing FIG. 11 shows portions 126 of the lead-to-lead spacing 122 whichhave been excised or removed in accordance with the embodimentsillustrated in drawing FIGS. 7B through 7E to provide the advantagespreviously outlined.

Turning now to drawing FIGS. 12 and 13, a small-footprint semiconductordevice 100 is shown with intermediate lead portions 112 having bottomlead surfaces 114 generally coplanar with the polymeric bottom surface116 of the molded package 120. The package 120 has a vertical groove 156aligned with each outer lead 118 such that the outer lead may be bentupwardly to fit within the groove. Between each groove 156 is a column157 of the package 120. Thus, the semiconductor device 100 will be nolarger, or just barely larger, than the molded package 120.

As shown in drawing FIGS. 12 and 13, outer leads 118A from the transfermolding process extend outwardly from the molded package 120. Verticalgrooves 156 are premolded or formed after removal from a mold. Eachouter lead 118A is bent upwardly at bend 118B. The outer end 118C isclosely fitted within the groove 156 near the top surface 117 of themolded package 120, and a portion 118D of the lead in the area of bend118B typically extends a short distance outwardly from the groove toprovide a bonding surface for lateral electrical connection to anothersemiconductor device, electrical conduit, or electrical apparatus. Eachgroove 156 is shown as extending to the top surface 117 of the package120, with a groove depth 152 generally about equal to the lead thickness132, and a groove width 154 slightly larger than the lead width 133,whereby the outer lead 118 will readily fit into the groove 156. Thus,the semiconductor device 100 has “surface” leads both on its bottomsurface 116 and on surfaces of the sides 119 and/or ends 142.

Portions of surface 114 which are to be bottom bonded may have adjacentpackage portions 126 excised or removed as previously described inaccordance with the embodiment illustrated in drawing FIGS. 7B-7E.

In drawing FIG. 13, the exemplary interior construction of the packageddevice 100 is shown as a chip-over-lead (COL) configuration, with chipor die 102 attached to inner lead 106 with an intervening insulativetape 158. However, as already indicated, the invention relates primarilyto the configuration of an intermediate “surface” lead and the outerleads; the invention may be applied to any interior chip-leadconfiguration for reducing the overall size of the device 100 andproviding both bottom and side/end lead bonding surfaces.

Another embodiment of the packaged semiconductor device 100 is shown indrawing FIGS. 14 and 15. The interior construction is depicted as achip-over-leads (COL) configuration with wire bonds 110. The entirebottom surface 114 of each inner lead 106 is coplanar with the bottomsurface 116 of the package 120. Portions of surface 114 which are to bebottom bonded may have adjacent package portions 126 excised or removedas previously described in accordance with the embodiment illustrated indrawing FIGS. 7B-7E.

While the outer leads 118 are shown as short leads like those of theembodiment of drawing FIG. 8, they may take any useful form such as theinverted-J leads illustrated in drawing FIG. 5, the lateral leads ofFIG. 12, or may be eliminated as outer leads as in drawing FIGS. 10 and11, depending upon the apparatus to which the device 100 is to beconnected.

In this embodiment, inner leads 106 are primarily supported by theiradhesive attachment to the insulative tape 158.

Drawing FIG. 16 shows a mold assembly 160 for encapsulating the die/leadframe assembly 162 in polymer to form the semiconductor package 120. Thedie/leadframe assembly 162 is shown as including a die 102, leadframe104, bond wires 110, and insulative tape 158.

The mold assembly 160 includes a top plate 160A and bottom plate 160Bwhich are closed together to form a mold cavity 164 therein.

Mold cavity 164 is defined by an inner surface 166A of the top plate160A and an inner surface 166B of the bottom plate 160B. A polymericencapsulant is introduced as a hardenable fluid through openings (notshown) as known in the art.

The top plate 160A and bottom plate 160B are configured to produce acasting or package 120 (see other figures) with an intermediate leadportion 112 and outer lead 118 having bottom surfaces 114 which arecoplanar with the bottom surface 116 of the package.

The mold assembly 160 illustrated in drawing FIG. 16 may be used to formthe packaged integrated circuit (IC) devices of the invention asdescribed herein. The particular embodiment of FIGS. 12 and 13 may haveits alternating pattern of grooves 156 and columns 157 produced aftermolding by cutting the grooves 156 by an erosion process or other methodknown in the art. A cutting apparatus having a plurality of spinning sawblades may be used, for example.

However, the particular groove/column pattern may also be produced inthe molding step, using a mold assembly 170 as illustrated in drawingFIGS. 17 and 18. A wall 168 of the top plate 170A which is intersectedby intermediate lead portions 112 has a pattern of alternating moldgrooves 176 and mold columns 178. During the molding process, the moldgrooves 176 are filled with encapsulant and become the package columns157. Likewise, the spaces occupied by the mold columns 178 become thepackage grooves 156 into which the outer leads 118 are bent upwardly.

While drawing FIG. 12 depicts the package grooves 156 with squarecorners, the preferred mold grooves 176 have angled groove sides 180 foreasy release of the hardened package from the mold cavity 172. Thegroove angle 182 may be any angle which permits rapid package release,but will generally be in the range of 5-15 degrees, depending upon thesurface roughness of the mold cavity 172 and the particular encapsulantbeing used.

In the manufacture of the semiconductor devices 100 of the invention,the steps involved include:

a. forming a leadframe with leads for the device;

b. preparing a die-leadframe assembly including electrical connectionsbetween the die and leadframe, any insulative layers, heat sink, etc.;

c. aligning the die-leadframe assembly within a mold assembly configuredin accordance with the invention by which bottom leaded portions have abottom surface coplanar with the bottom of the package;

d. closing the mold assembly and injecting fluid polymeric encapsulantto fill the mold cavity;

e. curing the encapsulant and removing the package from the mold;

f. deflashing the bottom of the package and portions of the outer leadsto remove flash residue from attachment areas of the leads;

g. lancing the leadframe to singulate the outer leads and/orintermediate lead portions; and

h. bending (if necessary) the outer leads to the specifiedconfiguration.

Following step f, the attachment areas of the leads may be plated withe.g. tin to enhance adhesion in a subsequent solder bonding step.

Where a package of the embodiment of drawing FIGS. 12 and 13 is to befabricated using cutting means to create the vertical grooves 156 in thepackage 120, such step will typically follow one of steps e, f, or g.

Where a package of the embodiment of drawing FIGS. 12 and 13 is to befabricated using a top mold plate 170A with an inner castellated wall168, the deflashing step may include deflashing of the grooves 156 inthe package, as well as connection surfaces of the outer leads 118.

Where portions of the package adjacent the intermediate lead portionsare to be removed, an erosion process or other method known in the artmay be used. This step will follow removal from the mold step e or asubsequent step.

In the lancing/singulation step, the outer leads are cut in conformanceto the particular embodiment, as illustrated in drawing FIG. 5 (fullinverted J-leads), FIG. 8 (abbreviated leads), FIG. 10 (leads cut atpackage surface), and FIG. 12 (abbreviated lead length).

This discussion and these figures presume and show a relatively exactingremoval of polymeric packaging material from adjacent the leads. As iswell known in the art, the methods of removing such material at theminiature scale will not generally leave precisely flat surfaces oruniform depths and angles. The embodiments of drawing FIGS. 7B-7E arerepresentative only and illustrate preferred constructions.

As described herein, the invention provides a semiconductor package ofreduced size, yet having leads for bottom and side/edge bonding orbottom and top bonding of the package. Thus, multiples of the device maybe vertically stacked in parallel, and/or be electrically joined in agenerally horizontal coplanar configuration. The invention may beapplied to a three-dimension-lead (TDL) package having outer leads onthe ends as well as the sides or top, together with bottom surfaceleads. The die/leadframe assembly shown and described herein isexemplary only, and may include other elements such as additional diesand leadframes, heatsinks, dielectric layers, etc., as known in the art.

It is apparent to those skilled in the art that various changes andmodifications may be made in the packaging methods and products of theinvention as disclosed herein without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:
 1. A mold assembly for encapsulating a die and leadframe of a semiconductor device in a polymeric package by transfer molding, comprising: a top mold plate having a pressure-resisting top and sides; a generally planar, pressure-resisting bottom mold plate configured to be sealably joined to said top mold plate, said top mold plate and said bottom mold plate together forming a mold cavity with a top, a bottom, side walls and end walls, said top and bottom mold plates configured to suspend a die and leadframe by said leadframe within said mold cavity for injection of encapsulant thereinto, wherein at least one of said walls has an inner surface castellated with vertically directed, alternating grooves and columns for forming columns and grooves, respectively, in an external surface of said molded package.
 2. The mold assembly of claim 1, wherein said grooves in the inner surface of said at least one wall have enlarged openings for release and extraction of a hardened polymeric package therefrom.
 3. The mold assembly of claim 1, wherein said grooves in the inner surface of said at least one wall have side portion surfaces angled to provide an opening dimension greater than an inner dimension of said grooves, said angle being in the range of 5 to 15 degrees. 